In the processing of round objects, it frequently becomes necessary to perform a subsequent operation based on an angular location on the object identified in a current operation. Normally, this requirement is achieved by placing a mark upon the object during the current operation. That mark is then used as a reference for positioning of the round object during the subsequent operation.
For example, in the processing of automobile tires and wheels, it is known to place a mark upon the tire at an angular location corresponding to the high point of the first harmonic of the radial force variation of the tire, and to form a valve stem hole on the wheel at an angular location corresponding to the low point of the first harmonic of the average radial runout of the wheel. During subsequent processing, when the tire is mounted upon the wheel, it is desirable to align the tire and wheel such that the marks are at the same angular location. This effectively reduces radial force variation in the resulting tire/wheel assembly.
However, physically placing marks upon the objects consumes cycle time and thus reduces process throughput. For example, in order to form a visible mark on the sidewall of a tire at a location identified by a tire uniformity machine, it is necessary to substantially stop rotation of the Tire with the high point of the radial force variation oriented in the direction of the marking device, and to then wait while the mark is applied to the tire. These steps can consume as much as 5% of the machine's cycle time on the average.
In other equipment, it has been known to reduce this consumption of cycle time by providing a second station on the machinery dedicated to carrying out the marking operation. While this second station adds expense to the machinery, it is nonetheless frequently beneficial to the cost effectiveness of the machinery to perform the marking operation at this second station. However, in tire uniformity machinery, it is not possible to accurately apply an angular mark at a second station of the machine. This is so because the tire must be "tripped" from the test rim of the first station and them moved to the second station; this causes loss of angular orientation of the tire.
It has therefore been a main objective of the present invention to provide methods of and apparatus for overcoming the difficulties associated with the current practices, and to provide a faster throughput in processing round objects such as tires and wheels.
It has been another object of the present invention to eliminate the requirement of marking round objects at a specific angular location.
According to the method of the invention an already-existing feature of the object is sensed in order to identify an angular reference. Thereafter, an angle indicating the position of the angular location of interest with respect to the angular reference is determined. Each of the foregoing steps can be carried out at a first station such as a tire uniformity machine without need of either braking rotation of the tire or of forming a new mark on the tire.